The present invention pertains to counterweights used in pumps and compressors, and particularly to counterweights used in reciprocating piston compressors.
Typically, compressors and pumps are provided with an eccentric affixed to the rotating shaft, through which the shaft is operatively connected to the compression mechanism for driving same. Centrifugal forces associated with the eccentric and/or the compression mechanism connected thereto must ordinarily be balanced to provide quiet operation of the compressor. Reciprocating piston compressors, such as the scotch yoke type compressor disclosed in U.S. Pat. No. 4,834,627, which is assigned to the present assignee, the disclosure of which is incorporated herein by reference, require counterweights rotatably fixed to the rotating shaft to reduce or remove force fluctuations associated with piston reciprocation and/or the forces acting on the pistons by the compressed fluid. The above-referenced scotch yoke compressor has its eccentric positioned between two journaled shaft portions, and has one counterweight portion integrally formed on the shaft located adjacent to the eccentric, between the eccentric and one of the journal bearings provided in the compressor crankcase. The other journal bearing is provided in a separate plate or cover removably attached to the crankcase, over an access or pilot hole through which the shaft is inserted through the first journal bearing and the assembly of the slide block and the other members of the scotch yoke assembly is performed, connecting the eccentric to the pistons.
To reduce the load on each journal bearing, it is preferable to have counterweights on each axial side of the eccentric. However, because of the necessary access for connection of the compression mechanism to the shaft eccentric, a second counterweight located adjacent the eccentric and between the eccentric and the portion of the shaft journaled in the removably attached cover or bearing plate may not be integrally formed in the shaft like the other counterweight is. The previous, above-referenced compressor therefore provides a counterweight attached to the axial end of the shaft, on the side of the bearing plate's journal bearing opposite the eccentric. The embodiment of the present invention shown in the figures is also a scotch yoke type compressor, similar to that disclosed in the above-cited U.S. patent. The counterweight attached to the axial end of the shaft of that compressor is, for background discussion purposes only, included in FIG. 1 and identified with reference numeral 10. Counterweight 10 is shown in ghosted lines and comprises no part of the present invention. The location of counterweight 10 is not optimal, for the counterweight attached to the axial end of the shaft and the integral counterweight are not located equidistantly from the eccentric. Both counterweights should be located equidistantly from the eccentric and between the two journal bearings to optimally load the bearings and provide quiet operation of the compressor. A way of providing a pair of counterweights on opposite axial sides of the eccentric and between the journal bearings while allowing access through the pilot hole for assembly of the compression mechanism to the eccentric is desirable.